FileCopy doesnt showing copied file progress on progressbar.Its showing while copy operation is completed

public partial class FileCopy : Form
{
  private BackgroundWorker bw = new BackgroundWorker();
 public FileCopy()
       {
           InitializeComponent();
           bw.WorkerReportsProgress = true;
           bw.WorkerSupportsCancellation = true;
           bw.DoWork += new DoWorkEventHandler(bw_DoWork);
           bw.ProgressChanged += new ProgressChangedEventHandler(bw_ProgressChanged);
           bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);

       }
 onstartButtonClick()
 {
   Thread readerThread = new Thread(new ThreadStart(readData));
   readerThread.Start();
   Thread writerThread = new Thread(new ThreadStart(writeData));
   writerThread.Start();
   writerThread.Join();
   readerThread.Join();
 }
 readData()
 {
   while (length > 0)
   {
    data = br.ReadBytes(data.Length);
    Buffer.putData(data);
    length = length - data.Length;
    Console.WriteLine("Reading {0}", data.Length);
    bw.ReportProgress(10);
   }
    Buffer.STOP = false;
    Buffer._reset.Set();
 }
private void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
       {
           this.BeginInvoke(new Action(() =>
           {
               Console.WriteLine("Inside Begin Invoke");
               progressBar1.Value = e.ProgressPercentage;
               Application.DoEvents();
           }));

       }
 public void writeData()
 {
    while (Buffer.STOP)
   {
     if (Buffer.STOP != false)
     {
          Buffer._reset.WaitOne();
          byte[] data = Buffer.takeData();
          if (data != null && Buffer.STOP == true)
          {
            fs.Write(data, 0, data.Length);
            fs.Flush();
          }
          Console.WriteLine("Writing to file :" + data.Length);
          Buffer._reset.Reset();
       }
   }
  }
}
 static class Buffer
   {
       public static  byte[] _data = new byte[10240];
       public static AutoResetEvent _reset = new AutoResetEvent(false);
       private static bool _isStop = true;

       public static bool STOP
       {
           get
           {
               return _isStop;
           }
           set
           {
               _isStop = value;
           }
       }
       public static void putData(byte[] data)
       {
           _data = data;
           Console.WriteLine("Data Length :" + data.Length);
           _reset.Set();
      }
       public static byte[] takeData()
       {
           return _data;
       }
   }